Photodetectors are well known in consumer and industrial electronics for detecting light and in response generating a signal proportional thereto. For example, photodetectors have been integrated with CCD image sensors to form linear and area arrays useful in video technology.
U.S. Pat. No. 4,473,836 (Chamberlain) discloses an integral large dynamic range photodetector element for linear and area integrated circuit imaging arrays. This prior art patent teaches a new CCD image sensor technology with a photoelement for providing input power detecting dynamic range greater than one million. The prior art photodetector has been used successfully to form wide dynamic range CCD linear image sensor arrays.
Subsequent improvements have been made to the aforenoted photodetector, as reported in the following publications:
1. B. C. Doody and S. G. Chamberlain, "An improved wide dynamic range silicon photodetector for integration in image sensor arrays" Canadian Journal of Physics, Vol. 65, no. 8, pp. 919-923, 1987. PA0 2. S. G. Chamberlain, B. C. Doody and W. D. Wahkurak, "A high photosensitivity wide dynamic range linear image sensor array" Electronic Imaging, pp.170-175, Mar. 28-31, 1988. PA0 3. W. D. Washkurak, S. G. Chamberlain, and N. D. Prince, "High Speed wide dynamic range linear CCD detector for acousto-optic applications" SPIE Symposium and Advances in Optical Information Processing, Orlando, Fla., pp. 1-9, Apr. 4-8, 1988.
Although the wide dynamic range CCD photodetector discussed in the above references is capable of producing a detecting input power dynamic range greater than one million in commercial CCD linear image sensor arrays, the prior art device nevertheless suffers from a number of technological limitations.
Firstly, as with other prior art photodetectors, the photosensitivity or NEP (noise equivalent power) of the above-discussed wide dynamic range photodetector is a function of its own capacitance.
Secondly, the above-mentioned capacitance of the prior art photodetector also results in slow speed of operation in the presence of short light pulses.
Thirdly, the prior art photodetector exhibits poor photosensitivity response in the presence of short incoming light power pulses.
Finally, during the charge transfer process of the video signal into the CCD readout shift register of the prior art photodetector, the signal may be contaminated, or smeared by the incoming incident illumination. Furthermore, blooming can also occur at high light levels.